Dermatoepidemiology. III. ABC principles for a critical review of the literature.

EPIDEMIOLOGY: Is the study of disease occurrence in human populations. As a science, epidemiology emphasizes descriptive and analytic observation, clinical trial, behavioral intervention, and the practical utility of diagnostic tests. "Epidemiology" is derived from the Greek epi (among), demos (people), and logos (doctrine).

CLINICAL EPIDEMIOLOGY: Is the application of epidemiologic principles and methods to problems arising in clinical medicine, dermatology included. For dermatologists, understanding this discipline is as important as mastering other basic sciences, such as immunology, microbiology, and dermatopathology. The recognization of Lyme disease is a classic work of "infectious" disease epidemiology. In 1972, a disease characterized by erythema chronicum migrans and "endemic arthritis" clustered in Lyme, Connecticut. By 1975, an infectious agent was suspected to be the cause of the disease. In 1977, the tick was thought to be the vector; in 1980, the spirochete became the prime suspect and, in 1982, Borrelia burgdorferi was identified as the etiologic agent. The study of hexachlorobenzene exposure, resulting in porphyria turcica, is an example of classic "chronic" disease epidemiology. The illness began in 1955 when sporadic cases of porphyria occurred in eastern Turkey. In 1957, the first case with illness resembling congenital erythropoietic porphyria was described. In subsequent years, over 3000 patients developed "epidemic" porphyria. The cause was due to the ingestion of seed wheat which had been treated with fungicides containing 20% hexachlorobenzene.

EPIDEMIOLOGIC

METHODS

For research, published elsewhere as Dermatoepidemiology. I., include descriptive observational study, analytic observational study, epidemiologic experimental study and tests for sensitivity, specificity, and positive/negative predictive value. Epidemiologic principles, instead, stress the correct interpretation of data, minimization of bias, and the appreciation of natural variations in collected data.